Technical Field
The present invention relates to a two-way communication technology between a digital microphone circuit and an audio control device, and more particularly to a digital microphone system, an audio control device, and a control method thereof.
Related Art
A microphone is a device capable of converting a sound wave into an electronic signal. Conventionally, the microphone is generally designed to be an analog microphone, which converts a pressure wave hitting an active surface of the microphone into an analog output signal by using a piezoelectric crystal, a capacitor, or the like, that is, the sound wave causes a charged diaphragm to vibrate, then the voltage of the capacitor plate is changed to generate an analog signal, then the analog signal is amplified, and then the amplified analog signal is transmitted to a recording device. However, the disadvantage of the conventional analog microphone is that the generated analog signal is very sensitive to external interference, so the quality of the analog signal is unstable and is strongly affected by external interference.
If the analog microphone is externally connected to or built in a computer system, capture and a transmission path of an analog audio signal are affected significantly by external interference in the system plane, for example, high-frequency noise generated by a high-speed operation on a Printed Circuit Board (PCB), seriously affecting the quality of the analog audio signal.
Therefore, a design of a digital microphone has been proposed in which a received analog audio signal is presented in a digital manner and then transmitted, so the influence of the external interference on the captured audio signal is reduced due to immunity of the digital signal to the noise. Basically, Please refer to FIG. 1, the concept of the digital microphone is as follows. Through a digital sampling mechanism, an analog audio signal generated by a digital microphone circuit 10 is converted in to a digital audio signal DATA, then an audio CODEC chip 20 is used to further perform a digital filtering operation, and then generated audio data in a digital format suitable for storage and play is transmitted to a computer system 30 for storage and play. Since the audio signal is already converted into a digital form at the beginning of receiving, the signal is not significantly polluted by various noise sources in the transmission path.
However, when an audio signal collected from the outside exceeds a gain range of a preamplifier of a digital microphone circuit, the audio signal collected by the digital microphone is distorted due to a too large gain. Additionally, restoration cannot be performed on the distorted audio signal through post-production processing of hardware or software. Conversely, when an audio signal collected from the outside is too weak and an amplification gain of a preamplifier is still relatively insufficient, although an audio CODEC chip or an audio controller can perform post-production processing to amplify the audio signal, noise of elements of the digital microphone circuit is relatively amplified, so that a signal-to-noise ratio (SNR) becomes small. In other words, since a transmission interface of the digital microphone circuit is a two-line transmission channel for one-way communication, the digital microphone circuit can only collect an audio signal according to set element performance (for example, a fixed pre-amplification gain), so that an energy range of the collected audio signal is limited.